Method for completing wells



o-age area of wells.

pressure in the well,

Aend of the tubing and be in turn connected Aother f raeturing liquid;

thepreferred embodiment, an electromagnet, leads 14 :as by clips to the tubing are connected across a battery 15 or other sutabl'e'supply power source may4V be fluid. herein referred to t as a fluid containing nely divided magttc triaten'als` t 2,695,063 Msrnonrori coMrrEriNo wnus Y and Gas Company, Tulsa, Okla., a corporation of Delaware r Appia-estro :une 12,1950, serais.' .isnaos 9 ciaim's. (ci. 1166-522) This invention pertains `to an improved method for treating wells. More particularly, this invention pertains to an improvement in vthe art of producing a fracture m afnrmatlon penetrated by a well to facilitate the recovery of fluids therefrom. Y j

Various methods have been proposed for increasing the productivity of water, oil, and gas wells; for example, nitroglycerin has been detonated in a well in some cases either to enlarge the well diameter or to fracture the formations immediately adjacent the well. Acid has been iniected into wells and into formations, particularly calcareous formations-'for the same purpose.

Wells have also been drilled laterally from a central bore for the purpose of increasing the productivity and drain- Fractures have also been produced in formations by the application of a high hydrostatic whereby the permeability of a formation adjacent a well and the drainage area around the well are increased. L

It is an object o f this invention to provide an improved method of completing wells by the process involving fracturing `a formation with fluid under high pressure. A further obiect -ofthisinvention is to provide an im'- proved method of isolating a' selectedV formation in a vwell and injecting a viscous liquid into that formation. A more specific object of this invention is to increase the viscosity of a fracturing fluid used in the hydraulic fracturing process by magnetic forces. These and other objects of this invention will become more apparent from the following description in whic reference will be made to the accompanying drawings. ln these drawings:- d

Figure l is a diagrammatic representation of a cross sectionof a vvell showing apparatus employed to fracture a formation in accordance with this invention; and

Figure 2 is across sectional view of one type of apparatus used in isolatingV a formation to be fractured and at the same time changing the properties of the fracturing uid so that v-it` has a vmore desirable filtrate rate.

The present' improvement in the processof fracturing formations consists in brief of 'temporarily isolating a formation bymagnetic means and injecting a fracturing a fracture. As indicated in Figure l, a Well 10 may be equipped with a tubing 11, which has associated therewith, at approximately the deoth of the formation which is to be fractured, a magnet-12. At the surface a high pressure, high volume pump 13 is connected to .the upper the suction line of this pump may to a source of, magnetic fluid or In case the magnet 12 is, as n the surface to vthe electromagnet may be attached 11. '--At the surface these leadsproperty of stilening when it isv4 mais@ aiifofa Clarence R. Fast,- 'tilsa, Okla., assigner tn Stanolind Oil producing formation is wherein the frictional forces lbetween the magnetic materials can be controlled by the application of a magnetic field. Besides this. magnetic material, the magnetic fluid contains a suspending liquid; I n the case where an o il to be fxactured,the liquid component ofthe magnetic lluidl is preferably oily.' Any.

mineral oil, lish oil, animal oil, or other oil-mscible liq an oil which` desirablev to uid can be used. A thixotropic oili. e; has'appreciable gel strength-is sometimes prevent the magnetic particles from Vsettling when the duid is in a quiescent unmagnetized state. Addition of a small amount of' such as oleic acid, to the oil produces oil from the formation itself can be eral, I have found that more viscous desirable.

this efect. Crude oils are generally l to about 10 centiposes, a viscosity inthe range -of f rom about 20 to about 200 or more cent-ipoises liquid into it under a pressure greatenough to produce t tions. vWhere thecore' general, the larger particle sizes are ythe'well. lhe magnetic lluid may has been found to be more desirable. oil, a steam cylinder oil, or the like are preferred oily liquid for the magnetic duid. lwater producing or water disposal formation an aqueous base liquid is preferred. I incorporate in this liquid the finely divided, highly permeable magnetic solid. Suitable solids are steels, eutecti: iron, carbon steels, and magnetic iron oxide. Other finely divided materials v .'hich exhibit magnetic propertie's, for example, cobalt, nickel, and molybdenum powders, may be used in place of the in general, these particles have a lower permeability than the iron powders and,l therefore, are less desirable.

The magnetic between about A lubricating and about 60 microns or more. In

permeability of a mixture of this material with a liquid is directly proportional to the particle size. The limit-v ing factor on maximum particle size is the ability to maintain-the particles in suspension-the more viscous the suspending liquid, the larger the particles it will suspend,

The ratio of magnetic material to liquid may be varied over a substantial range. I have foi-ind, however, that the ratio of from about l material to l part of liquid by weight produces satisfactory fracturing liquids.

Since the permeability of the fluid increases with an increase in .the ratio of magnetic t material to liquid, higher ratios of magnetic material'to liquid are preferred. Pumpability of the magnetic Huid fracturing liquid appears limits the maximum ratio of magnetic material to liquid and pumability of the fluiddepend's, among other things,

the particle size, the liquid, and the like.

upon the pump, There appears to be no minimum concentration of magnetic material in the oil except that at low concentration's the permeability of the magnetic duid becomes relativelylow, thereby decreasing the viscosity of the .fluid under a magnetic field. A ratio of magnetic material to liquid of greater than about 5 permeability of the magnetic fluid is generally the element which determines the minimum concentration of magnetic material in the liquid. A permeability of greater 'i than about 3 in'c. g. s. units is considered operable in most cases; however, I prefer a permeability about 5. The ratio of magnetic material therefore, be adjusted for each set of circumstances.

These particles are incorporated 'in the liquid vsuitable means; for example, by stirring or by a iet-type mixer. This magnetic llud is displaced into the fivell 10 through tubing 11 by pump 13. T he tin-id,- due to the inclusion ofthe iron particles, is generally more dense thanthe'well duid and, therefore, strained, appears to displace the well fluids upwardly in be placed the well before the magnet 12 is lowered into the well orpin the case of an electrinagnet, before it is energized. l have found it generally desirable, however, to energize the magnet before the magnet fluid is wellI to prevent loss of 'the magnetic raus-@Gti Panarea '1 as4 a highly polar surface-active agent,

used; but, in gen' Whereas crude oil may have a viscosity of examples of the In case ofa hydrogen-reduced iron, hypo-euteetcid i steels, hyper-'cutectoid steels, carbonyl iron powders; but,

material is ground to a particle'size of preferred since the to about 1 0 parts 'magnetic to be the only factor whichl i's preferred'. The

of greater than to liquid must,

unless otherwise conimmenenti inw die fluid to the forn'iaf' of an electromagnet is highly-vv therefore, the flow of the magnetic material -corev is not materially retarded by the magnet. Neary the end of themagnetic coil, which is preferably placed near `the enti of th'e tubing, the magnetic field has its maximum intensity. .'Iherefore, the frictional forces be- '.,permeableflas-for example, where the -eore' iscon-4 s-tructed of tubular magnetic material such as iron, the.

magnetic field within the co're is substantially zero and,

tween the magnetic particles, i. e., the 4viscosity of the magnetic Ifluid, are greatest around the end of the tubing through the The extreme viscosity or set of the magnetic lfluid prevents the magnetic tiuid from flowingupwardly around the tubingthe viscous-fluid in this region functioning like a.

I packer between the ,tubing and the well wall. This high viscosity is generally yadequate' to prevent nov/ of the magnetic uid into the annulus between the tubing and the 'well wall, but a packer may occasionally be set in this area to advantage. Magneticiluid issuing from the tubing is by comparison `substantially less viscous than the magnetic uid between the tubing and the well walls. T

Accordingly, this magnetic fluid flows into and fills the confined zone in the well below the end of the tubing.

s' 'Ihe zone may be limited at the lower end by the bottom of the well, by a packer,l a plug, another magnet, or other means well known in this art. The magnetic field from magnetlZ extends` into this fluid and thereby inl creases its viscosity.` This increased viscosity prevents the magnetic fluid from penetrating the pores of the formation. f

If injection of the fluid is continued after the confined zone becomes filled with viscous magnetic fluid, hydraulic pressure on the fluid rises until the strength of the formation is overcome vand a fracture 17 results. The hydraulic pressure in the confined zone necessary to produce a fracture has Abeen found to vary in wells 2000 ft. or more in depth from about 0.7 to about 1 lb. per foot of well depth. This pressure of the magnetic fluid required to fracture a formation'is hereinafter referred4 to as the formationlbreakdown pressure. It is generally recognized `by an observation of the pressure in the. tubing. After -the confined zone becomes filled with magnetic fluid, the pressure rise, assuming a volume of two or more barrels per minute, is roughly propertional to thevolume ofthe fluid injected into well. After the formation fractures, theprcssure risc ceases to be proportional to the volume of the fluid injected into the well. In fact, in yrnany cases, the pressure may decrease sharply when the formation fractures even though thereis no decrease in the fluid injection rate. -The pressure at which this change in the slope of a pressurel versusvolume curve' occurs is the formation-breakdown pressure. After the formation fractures, the magnetic fluid enters and the fracture may be extended a' substantial distance from the well by Acontinuing to pump fluid into thev well. It appears that whereas the field strength of the magnet and the viscosity of the magnetic fluid are greatest adjacent the end of the magnet, the viscosity of the magnetic fluid may be maintained'reasonably highfor a substantial distance into the formation due to the relatively high permeability of the magnetic fluid in comparison to the permeability of the rocks. That is, -theflux lines of the magnet appear to be concentrated in and to follow the lens of magnetic material and to return to the tubing form great distances through the rocks. Obviously, the viscosity of the fluid gradually decreases with distanceb from the magnet as the eld decreased. Once a fracture has been initiated. the pressure required to extend it is generally reduced and therefore, the fracture appears to be extended several feet-into the rocks even though the flux density, andv therefore the viscosity of the uid, ismuch less at this distance than in the well at the end of the tubing. The.

viscous and the' liquid ltersiinto the formations sur-if.vv

roundingthe frcture,allowing the' granular particlesL to' p These particles then supf,v port the overlying formations and maintain a highly:`

fluid-permeable. path from the formation into the well.. The liquid, being in the preferred embodiment miscible be deposited in the fracture.

with the liquid in 'the formation, may th'en be produced with the well fluid, as'by flowing, swabbing, or pumping the well.

The magnetic field *may be produced, as indicated -l Y.

above, by a'number-of. types of apparatus. 'In the case of an electromagnet the magnetic field may be produced or discontinued at will, whereas in the case of a pet-l marient magnet the magnetic field is continuous.

electromagnet is", therefore, preferred since the removal of the tubing may be facilitated by de-energizing the* I:

magnet and 'reducingthe viscosity of the magnetic fluid before'removing the tubing. Even though the viscosity of the magnetic fluid is not reduced, however, the tubing the tubing in the well.

moved through this viscous mass ifsufiicient force is ap and magnet may be removed fromv the well by the application of a suitable force. It appears that, upon the application of'a magnetic field, the magnetic particles in a magnetic fluid come into contact with each other p roducing a quasi rigid 'or very viscous connection between the magnet and the well walls thereby tending to freeze The magnet can, however, be

plied.

to vthe lower end of tubing 1l. Where alternating current is applied to. the magnetic coil 22 at the lower end of the sub, the sub is preferably constructed of a strong nonconducting material such as plastic. However, where direct current is used to energize the coil, the s ub may be constructed of brass or other non-magnetic metals.

While Vthe non-magnetic sub is obviously desirable, it is flux density is`g'enerally maintained'as high as' possible in the well consistent with sound. engineering design of permanent or electromag-n -ts so that the fracture can be extended to great distance.

Any amount of magnetietluid may be injected into the fracture. For example, from about 100 to about 5000 gallons or more may be used, but it appears thata 1000 g'A lontreatment on the average is about the rnost'de-v sirable considering. cost and results.

After the magnetic fluid hasl been iniected into the fracture to the desired distance, the electromagriet may be de-energized by opening Vswitch 16. 'Any magnetic -tluid in the well 10 and fracture 17 then becomes less not necessary since it 'merely assists in concentrating the- Coil 22 is connectedvia' leads 14 to -a source of electrical energy' as above def scribed. The coil is wound on a magnetic core 23 hav-v magnetic field from the coil'.

ing upper pole piece ,24 and lower pole piece 25. T hese pole pieces and the core may be laminated to advantage where A. C'. power is used. Lower pole piece' 25 mayi be a circular plate which closes thelower end of. the

tubing. A number of uid outlets 26 are'provided around the periphery of the tubular core' and extending through the coil; These conduits may be threaded into the tuf bularcore as indicated. They are preferablv constructed of a non-magnetic material such as .brass so as not to atleet the magnetic field produced by the coil.

`In operation this apparatus is lowered into the well, i i

as described in connection with the embodiment shown in Figure l, the coil is energzed,'and the magnetic fluid is injected through tubing 11, non-magnetic sub 21, Vand fluid outlets 26 into thel well. Since the magnetic field is substantially stronger adjacent the pole pieces, the magnetic fluid in the well contiguous tothese p'ole pieces has a viscosity much greater than the viscosity of the4 magnetic lluid in the intermediate zone. In fact, the magnetic fluid adjacent the pole pieces may withhigh lieid strength be made practically rigid thereby preventing the escape rif-magnetic fluid vinto the well above and below the p'ole pieces. Being rigid-not only prevents flow of the magnetic fluid into the well above and below the coil but also prevents it from flowing intothe formation at these' points. Since the reluctance of the flux path through the formation is roughly equal to the reluctance of an air path`,"the magnetic field between the pole pieces extends out from the coil 'through the formation and the flux' density decreases as a function'of the radial distance from the pole pieces. The depth of penetration of the flux path into the formation is dependent on the ampereturns in the vcoil and on the length of the coil. Accordingly, high power input to the coil and a long coil, e. g.,

from about 5 to 20 ft. or more, are preferred. The visl' cosity of the magnetic Huid around the coil is thus yiucreased to some extent so that it does not readily. pene trate .the permeable formations-the magnetic fluid in etect having a low filtrate rate due to` theforces between -An alternative type of apparatus particularly adaptedi; to fracturing formations is shown in Figure 2. In this Y kembodiment a nom-magnetic tubular sub 21 is attached the magnetic particles in the liquid. Since the, magnetic fluid -in the zone surrounding theenergized coil has a.

low filtrate rate, it `will not be lost intothe forrriatioItI'-` when a high pressure is applied. permits 'theformaf use different fluids for the two functions.

field and recovering fluids from said formation. A

tion'-brealdowirl pressure to be built up so that afracture can be initiated.A

The magnetic field from coil 22 extends into the forma;-

tion a substantial distance, the strength of this field, and

accordingly the viscosity of the magnetic fluid, beinga function' of the distance. In somecascs, the magnetic fluid enters the formation in a lens which is much closer s. A marsa of increasing the-productivity of a f ormaj tion penetrated-by a well comprising placing an electromagnet in said well on a string of pipe, energizing said electromagnet, injecting a magnetic fluid into said well through said string, said fluid issuing from said pipe in said well in the magnetic field of saidelectromagnet .being substanto one poleA piece than to the other so that the highly permeable pole piece is, in effect, extended out into the formation by the relatively high permeability magnetic fluid.. The magnetic flux leaving one pole piece would then. extend in a concentrated path through this .lens out into the formation and would return to the other pole piece through the high reluctance formation. 'I hus, by.

t the embodiment illustrated'in Figure 2, an intermediate zone in a well can be isolated from the remainder'of the Afore the viscosity of the magnetic f luid in this zone is.

more easily controlled. y

This invention has been described above with particular reference vto fracturing a formation with the magnetic fluid which thus performs two functionsboth isolating and fracturing a formation. ln some cases itis desirable to found it particularly advantageous to first surround the magnet or magnets with magnetic fluid, stifien this fluid at points in the well by energizingthe magnet or magnets,

and then inject a fracturing liquid into the zone isolated by l Y the magnetic fluid. The second or fracturing liquidmay fluid issuing from said pipe and flowing -into a zone to be v l isolated bci-ng less viscous than .said fluidA in said annulus v ,well and the adjacent' formation can be fractured by a tially solidified in the annulus between said string and the walt of said well to isolate av zone of said well and said vbetween said string and the wall of said well, applying a high pressure to said fluid within said isolated Lone-to 'fracture said. formation in said zone, de-energizing electromagnct, andwithdrawing said pipe and said elec- 'tromagnct from said well.

6. A 'method of increasing the productivity of a formation penetrated by a wellcomprisihg disposing on a string of pipe in-said well an electromagnet having disc-type pole pieces of slightly less diameter than said well, disposing a magnetic fluid in said well around said electromagnet, energizing said electromagnet to incrcase'the viscosity of said magnetic fluid, the viscosity of said magnetic fluid adja- That is, I have cent said pole pieces being substantially greater than its viscosity in thezone between said polepieces, applying `ay high pressure to the viscous fluid in 'said zone to fracture said formation, pumping saidtluid into said formation to extend said fracture, de'ener'gizing said electromagnet to -decrease the viscosity of said fluid, and producing `said well. A

7. A method of increasing the'productvity of a formation penetrated by a well comprising injecting 'into said well a magnetic fluid containing from about 1 to about l0 parts by weight of a powdered magnetic material in l part' of an oily carrier, disposing a magnet in said well adjacent said formation at the boundary of a-.zone to be isolated to set said fluid at said boundary, .and injecting a 'gelled oily liquid into said formation wi-thin said zone-at the formation-breakdown pressure to fracture said formation.

8. A method of increasing the productivity of a formation penetrated by a well comprising injecting into said Well a magnetic fluid containing lfrom about 1 to about 104 parts by weight of a powdered magnetic material in l part of an oily carrier, disposing an electromagnet in said well adjacent said formation at the boundary of a zone to be isolated, energizing said electromagnet to set said fluid at said boundary, and injecting an oily liquid containing a hydroxy aluminum soap into -said formation within said zone at the formation-breakdown pressure to ticular magnetic fluids described. -lnstead this invention should be limited in scope only by the appended claims.

I claim:

l. A metliod of temporarily plugging a well comprising fracture said formation d'e-energizir g said electromagnet, and, after the viscosity of said oil'I liquid containing a hydroxy aluminum soap has been substantially reduced, recovering fluids from said formation.

9. Av method of increasing the productivity 'of a well comprising creating a strong magnetic field in said-well, in-

` jecting a magnetic fluid into said well to set saidvmagnetc tion penetrated by`awell comprising creating a strongmagnetic field in said well at a point adjacent said formation to isolate a-,zone 4in said well opposite said formation, injecting a magnetic flued into said well at said point, following said magnetic fluid with a liquid containing a bodying agent which is injected into said formation at a o pressure as great as the formation-breakdownpressure, discontinuing said magnetic field and recovering fluids from ysaid formation. l

3. A method of increasing the productivity of a formntion penetrated by a well comprising creating a magnetic field in said'well and in said formation adjacent said well,

injecting a magnetic -field into said formation at the forma' tion-breakdown pressure,r discontinuing said magnetic field and recovering tluids`from said formation.

4. A method of increasing theproductivity of a forma tion penetrated by awell comprising disposing a magnetic fluid in a well, inducing a magnetic field in said fluid to in.

crease its viscosity, applying a pressure atleast'as great as, the formation-.breakdown pressure to said fluid to inject pages 11374140. -tCopyi'nPatent Qfce Library. said fluid into sad`formaton,discontinungsaid magnetic vfluid and isolate a zone in said well, injecting a liquid into a formation within said zone which is isolated to increase the permeability'of said formationLand discontinuing said magnetic field whereby said fluid may be recovered from said welL References Cited in the file onf-this pa'tent UNirED' STATES PATENTS Date A Number Name Y 2,033,560 Wells ...'.,t.. Mar. 10, 1936 2,033,561 Wells Mai'. 10, 1936' K 2,107,006 Lang Feb. l, 1938 g Y 2,354,570 Benckensteiri uly 25, 1944 f v OTHER REFERENCES Y new.:

'ni on and Gas Journal, october i4, Isitapage; 76; jl

78. (Copy in 16S-2l, Division 49.)

Bureau of Standards Bulletin, June i949, pages 74476. I

(Copy in 175-21 Magnetic Fluids, Division 4S.) Journal of Applied Physics, vol. 20. December 1949,. 

2. A METHOD OF INCREASING THE PRODUCTIVITY OF FORMATION PENETRATED BY A WELL COMPRISING CREATING A STRONG MAGNETIC FIELD IN SAID WELL AT A POINT ADJACENT SAID FORMATION TO ISOLATE A ZONE IN SAID WELL OPPOSITE SAID FORMATION, INJECTING A MAGNETIC FLUID INTO SAID WELL AT SAID POINT, FOLLOWING SAID MAGNETIC FLUID WITH A LIQUID CONTAINING A BODYING AGENT WHICH IS INJECTED INTO SAID FORMATION AT A PRESSURE AS GREAT AS THE FORMATION-BREAKDOWN PRESSURE, DISCONTINUING SAID MAGNETIC FIELD AND RECOVERING FLUIDS 